This invention relates to a mine prop headboard that can be used to support a preload bag.
Elongate mine props, typically timber-based, are widely used to provide yielding support to the hanging wall in mine stopes. Conventional practice is to trim the prop to length in the stope and then to tilt it to an upright orientation between the footwall and the hanging wall. Timber wedges are then hammered into position between the hanging wall and the top of the prop. The wedges have a dual purpose. Firstly, they serve to wedge the prop in position to prevent it from falling over during blasting. Secondly, they are employed to apply a degree of axial preload to the prop.
It is highly desirable to apply a fairly large axial preload force to the prop at installation, since this will immediately render the prop suitable to take the working load of the hanging wall as the hanging wall closes towards the footwall. However preload force applied by wedges as described above is very much less than that which is desirable.
It has therefore been proposed to provide the prop with a headboard on which an inflatable bag can be supported. During installation, the bag is positioned in a deflated condition on the headboard, between the head of the prop and the hanging wall. The bag is then inflated to a substantial pressure with a settable grout with the result that a substantial preload force, possibly in the range 10t to 20t, is applied axially to the prop.